What should I do about this weird crush?

I have a crush on this guy who works on a bookstore I go very often, I was talking to a guy and he walk by and when I look at him he look down at the floor, I was looking at some books when he walk in and I don't know why I felt like looking back and when I did he was there and we look at each other for a second, yesterday he walk by me a few times and I did by him but I couldn't bear to look at him I only look at him when he was busy not to notice me.